Red-emitting phosphors based on complex fluoride materials activated by Mn4+, such as those described in GB 1360690, U.S. Pat. Nos. 3,576,756, 7,358,542, 7,497,973, and 7,648,649, can be utilized in combination with yellow/green emitting phosphors such as YAG:Ce or other garnet compositions to achieve warm white light (CCTs<5000 K on the blackbody locus, color rendering index (CRI) >80) from a blue LED, equivalent to that produced by current fluorescent, incandescent and halogen lamps. These materials absorb blue light strongly and efficiently emit between about 610-635 nm with little deep red/NIR emission. Therefore, luminous efficacy is maximized compared to red phosphors that have significant emission in the deeper red where eye sensitivity is poor. Quantum efficiency can exceed 85% under blue (440-460 nm) excitation.
While the efficacy and CRI of lighting systems using Mn4+ doped fluoride hosts can be quite high, one potential limitation is their susceptibility to degradation under use conditions. It is possible to reduce this degradation using post-synthesis processing steps, as described in U.S. Pat. No. 8,252,613. However, development of alternative methods for improving stability of the materials is desirable.